Turn on thread page Beta
    • Thread Starter
    Offline

    1
    ReputationRep:
    Could someone please explain rigid objects in equilibrium please, I have no idea how to do these questions. Example question:
    Q) A uniform rectangular picture ABCD, 3 metres wide and 2 metres high, has weight 400 newtons. It is supported on a trestle at a point E of DC, 1 metre from D, and kept upright by means of a rope attached to the picture at A. Calculate the tension in the rope and the normal and frictional forces at E.
    a) if the rope is horizontal
    b) if the rope is held at 40° to the vertical
    Picture below might make things a bit clearer. Thanks for any help (Rep goes to most helpful)

    ANS:
    a) 100N, 400N, 100N (I got the 400N)
    b)97.5N, 475N, 62.7N
    Thanks again
    Offline

    0
    ReputationRep:
    for a)
    Weight left of E = 400/3 = 133+1/3
    W right of E = 2*400/3 = 266+2/3
    Take moments about E:
    2T + .5*133+1/3 = 1*266+2/3
    T = 100N
    Resolve vert:
    Normal = 400N
    Resolve horiz:
    Friction = 100N

    Hope thats clear enough
    Offline

    15
    ReputationRep:
    a)
    taking moments around E
    anticlockwise moments = clockwise moments
    TN*2m = 0.5m *400N
    T = 100N

    400N is the normal reaction

    the friction at E is the force that will balance the whole system.
    the tension in the rope is providing a force of magnitude 100N to the left. the only force available to counter this is frction which will thus have an equal and opposite value: 100N to the right.

    is there a diagram for part b? tis a bit confusing
    • Thread Starter
    Offline

    1
    ReputationRep:
    Thanks a lot, that makes sense. I just wasnt doing the moments properly because I wasnt sure how to take moments when the Tension was horizontal and the weight was vertical. But I guess its just a case of seeing the effect they have (ie horizontal tension pulls it A-clockwise and the weight pulls it clcokwise).
    As for the picture, sorry thats the only on in the book. What I think it means is that the rope is held upwards and the if the line DA was extended upwards then there would be an angle of 40° between the line and the rope. Ill let you know if I manage to get the answer.
    Thanks for the help
 
 
 
Turn on thread page Beta
Updated: June 21, 2005
The home of Results and Clearing

2,170

people online now

1,567,000

students helped last year

University open days

  1. SAE Institute
    Animation, Audio, Film, Games, Music, Business, Web Further education
    Thu, 16 Aug '18
  2. Bournemouth University
    Clearing Open Day Undergraduate
    Fri, 17 Aug '18
  3. University of Bolton
    Undergraduate Open Day Undergraduate
    Fri, 17 Aug '18
Poll
Do you want your parents to be with you when you collect your A-level results?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.